Why is there a milky brown oil layer in the coollant reservoir of my Mazda MPV?


Asked by Ronel Aug 11, 2014 at 05:44 PM about the 2003 Mazda MPV

Question type: Maintenance & Repair

When my husband checked the coolant there was a milky brown layer of oil floating on
top. The car was running fine.He took it to mechanic and there was a small pipe leaking
he fixed that but is puzzled about oil as he can find no apparent fault.

20 Answers


There are many ways that can happen. Bottom line it was oil from the engine mixing with the coolant. And it was a cheap fix. Not a head gasket.

15 people found this helpful.

Do you know if it had any head work done in the past? It is possible that something may have happened in the past and the cooling system didn't get completely cleaned out. I had a Mazda 323 that was like that, it took a couple of times with a cooling system flush machine to get all of the oil out of it.

5 people found this helpful.

... Or you have a weak or blown head gasket.

1 people found this helpful.

Well tennisshoes, the only thing we had recently done was an oil change and check at Jiffy Lube, before that absolutely no problem. The weirdest thing is that when we start the car it purrs like a kitten it does not sound like anything is wrong, we also did a computer check at the auto shop everything seems normal. We flushed it twice now and it was clean but now there is more oil. What other symptoms are there for a blown head gasket, will the car even run?

4 people found this helpful.

Has anyone ever used Steel Seal? Should we or not try this?

3 people found this helpful.

Do NOT use anything like that, it causes more problems than it fixes. Some of the symptoms of a blown head gasket are: a lot of white smoke out of the tailpipe when first started, an engine miss when first started then it clears up and runs fine. As you don't have any of those look at the oil cooler for a possible internal leak, examine the oil in the cooling system closely, is it engine oil or auto trans oil, you may have to flush it again to find out, but brown is usually engine oil, there could be internal engine problems like a crack in the block or a casting flaw that finally let go, could also be a cracked head that is not in the combustion area. It may take a exploratory tear down to find the trouble.

1 people found this helpful.

Ouch! That sounds serious! There is no white smoke or engine miss, the oil is not reddish so it is not transmission oil. The engine oil does not go down at all. I guess you are right, a exploratory tear down might be it. That will probably be very expensive :( Oh man!


How many miles are on the vehicle? It is 11years old, you could think about just replacing the engine with a used one, might be cheaper than a tear down, or even a rebuilt engine if you plan on keeping it. HTH

1 people found this helpful.

I am not sure about mileage, I so want to keep it it is such an awesome vehicle. Very good on gas too. We will have to look at our options, my husband is currently working in Jacksonville, FL and the MPV is our only car, at the moment. Thank you so much for your advise.

1 people found this helpful.

So it turned out that the oil changing place actually added some oil to the coolant reservoir! After flushing the system 3 times there is no more oil at all in the coolant. Thank heavens!


WWWAAAHHHTTT? That is something a high school kid does, I hope they are going to reimburse you for flushing the system and some free oil changes.

1 people found this helpful.

Unfreakin believable. I'm relived that you got to the bottom of this, but how did you find out? Did you have to water board Jiffy Lube?

Best Answer Mark helpful

He he, Mark you are funny! Anyway it is a long story and our mechanic got to the bottom of it all after gasket tests and all sorts of checks, when he heard where the car went for the oil change he knew immediately. He said the same thing happened to another client of his. I believe the company does radiator flushes and they probably need more business! Anyway we are just relieved that there is nothing wrong and we caught it in time, we flushed the system and the car is running great, mystery solved. I believe my husband will still pay a visit to them to inform the manager about this but we will not charge them as it did not cost much to fix. Silly negligent people! :)


I would incurage you fire if a letter to there corporate office. You were able to get to the bottom of the problem by determination and preserving. You knew something didn't add up. Think of the retiree that lives on a limited income and is going to give up something else to pay for a $99.00 radiator flush that they don't need. Old farts like me are dependent on our cars and in many cases it's our freedom.

2 people found this helpful.

Yes Mark, we will do that. I agree the bosses should know what is happening. Thanks for that advice.


I am an ex mechanic from NJ and I am having the same issue with milky coolant in the overflow tank, I thought it was the head gasket at first as most would but no other signs. After checking the cooling system I found that the oil cooler just above the filter had gone bad, coolant and oil were mixing. I talked to an mechanic at Mazda and he told me that this was common with MPV and some other models.

11 people found this helpful.

I know this is really old and you all are probably never on here anymore. But my 08 is having this exact same problem. No white smoke runs and puts like a kitten, pulled the oil plug and no antifreeze in it. But my resvrior is full of oil and is now in a radiator. (I do my own oil changes, and my husband and I already replaced the cooling unit in april (never will get a part from rockauto again).


So by the cooling unit you mean the oil cooler? If so then double check the gasket and seals as they maybe leaking internally. If that checks then you may very well indeed have a blown head gasket or a cracked cylinder head. But you still need to deal with the oil in the engines cooling system after repairs are done. You will need a very good flushing solvent to get the oil, as there are so many out there ask a parts guy on what he recommends, or if you went with a shop doing the repairs that they have a reverse flow flushing machine cause by now it is also inside the heater core.

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